This invention relates to circuit components mounted on circuit boards by solder column interconnects or arrays, and more particularly, the support of circuit components having column grid arrays.
Solder column interconnects or arrays are used to interconnect circuit packages to circuit boards, most typically large ceramic integrated circuit packages. One such package is the column grid array (CGA) integrated circuit package that has a ceramic substrate with an array of solder columns that extend out from it, typically from the bottom surface. The solder columns are attached at one end to connection pads or locations on the ceramic substrate. The solder columns are sufficiently tall so that when the circuit package is placed on a circuit board, the solder columns can accommodate the difference in thermal expansion between the ceramic integrated circuit package and the printed circuit board. The solder columns are soldered to respective pads on the circuit board using known techniques, such as a convection reflow solder process.
One problem with solder column arrays is that the solder columns do not withstand compressive force well. The solder columns in the solder column arrays are typically made of a 90%/10% Pb/Sn solder, making them soft. Moreover, the individual solder columns are very thin. Consequently, if any significant amount of compressive force is applied to the circuit package, such as might be applied by a cooling solution such as a heat sink or fan, the resulting weight on the circuit package may cause the solder column array to compress, particularly over time, which may compromise reliability. In this regard, loads in excess of about 10 to 20 grams per column exert sufficient compressive force so that reliability may be compromised. Since CGA integrated circuit packages are being increasingly used for high power integrated circuits, the cooling solution required often has considerable mass. It is not unusual for the heat sink or cooling solution used with such high power integrated circuits to exceed one pound.
In accordance with an aspect of the invention, a circuit board assembly has a circuit board and an integrated circuit package having a substrate with an array of solder columns extending from a bottom surface of the substrate to the circuit board when the integrated circuit package is mounted on the circuit board. At least one support member is affixed to at least one of a side of the substrate and a top surface of the substrate when the integrated circuit package is mounted to the circuit board. In an aspect of the invention, each support member is affixed by adhesive after the integrated circuit package is mounted to the circuit board, the adhesive accommodating any variation in height of the integrated circuit package. The support member or members support the integrated circuit package against compressive force.
In an aspect of the invention, the integrated circuit package is a CGA integrated circuit package.
In an aspect of the invention, the support member is a frame that surrounds the integrated circuit package and is affixed thereto. At least a portion of the frame extends from the substrate to a portion of a circuit board assembly when the column grid array integrated circuit package is mounted on the circuit board. The frame supports the column grid array integrated circuit package against compressive force.
In an aspect of the invention, the frame includes flanges that extend over a top surface of the substrate and that are affixed to at least one of the top surface of the substrate and an outer perimeter of a lid of the integrated circuit package.
In an aspect of the invention, the frame is affixed to at least one of an outer perimeter of the substrate and the outer perimeter of the lid.
In an alternative aspect of the invention, support legs support the substrate and have a flange that is affixed to at least one of the top surface of the substrate and an outer perimeter of the lid of the integrated circuit package.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.